OAL and accuracy

[esheato]

I experimented a bit with OAL using my Cooper MTV in .223 AI today.

Using 40 grain Sierra BlitzKings and fireformed brass, I loaded five cartridges with the following OALs (measured using a Sinclair comparator):

2.805
2.825
2.845
2.865
2.885
2.905
2.925
2.945
2.965

Now for the record, the leade on this gun is so long that I can't determine the max length with the short 40 grain bullets. It doesn't matter much anyway, as the numbers are only relevant to this rifle.

The group on the top left had the bullet seat the farthest from the lands. As the bullet was moved closer and closer the groups tightened significantly.

 

[BluesBear]

Looks like the less jump the bullets have to make to reach the rifling the better they fly.

Hopefully you'll try the same thing with 62gr.

 

[esheato]

Blues,

I already have. The 1 in 14" twist keyholes with the heavier bullets.

Thanks for responding though.

Ed

 

[BluesBear]

Ahhhh. I see. I didn't realize it has a 14" rot.

Did you have similar results with 50-55gr? They should still shoot well with that rate.

 

[esheato]

The 50 BlitzKings did well, but I went with the 40's due the increase in velocity. It really splatters squirrels.

Ed

 

[dakotasin]

i see you have a group wrecking flyer in almost every group! the good news is that you are probably not the problem. the bad news is flyers suck! lol! at any rate, putting that many nice groups together is tough to do. nice work!

i've run similiar tests in my guns as well, and have come up w/ similiar results - the closer to the lands, the tighter the group. i've also taken this a step further, starting deep and getting closer, and then going into jam, and on into deep jams into the l&g's.

some rifles like a hard jam, and others fall apart. i don't come up w/ a hard correlation. but, as most of my guns are hunting rifles, it doesn't matter because it is bad practice to seat hunting rifles into the l&g's.

 

[The Bushmaster]

At what distance were these fired from...?

 

[dakotasin]

i don't know for sure, but given they are all roughly 1" high from a rifle, i would assume they are 100 yard groups.

 

[~z]

esheato, Where did you get those targets?
~z

 

[The Bushmaster]

Hmmmmm...You have a point. dakotasin.....

 

[esheato]

i see you have a group wrecking flyer in almost every group!

dakotasin, my good man...I knew you'd be along to remind me. I think it's more a function of my unconscious mind telling me I'm going to pull one shot of every group...

The cases are Remington (should have used the Lapuas but I wanted to see relative accuracy for a varmint hunt type of load) and they're filled to 85% capacity. The propellant (H322) is weighed on a digital scale. Bullets seated using a Redding Competition Die and measured using a Sinclair comparator. Primers are Federal Gold Medal Match which are hand seated using a Lee tool.

Where's my weak link? Propellant? Primer? Hmmm....

At what distance were these fired from...?

104 yards measured by my Leica

Where did you get those targets?

Sinclair International, page 3

 

[NVMM]

Nice post. Thank You